What of the following best describes the relationship between developing nations clean water and human health

Below are the choices:

A. Many developing nations lack access to clean water; this can harm human health.
B. Clean water is never available in developing nations, so human health is always a major issue there.
C. Human health does not depend on clean water; health issues in developing nations are not related to water.
D. Contaminated water and human health is not a problem in developing nations, but it is a problem in developed nations.

The answer is A. 

You need to do x2-x1,y2-y1 and divide it by 2 and you should get (1,-3)